Well, although I have 7 now per node, you make a good point and I'm in a position where I can either increase to 8 and split 4/4 and have 2 ssds, or reduce to 5 and use a single osd per node (the system is not in production yet).
Do all the DC lines have caps in them or just the DC s line? -Tony On Sat, Feb 28, 2015 at 11:21 PM, Christian Balzer <ch...@gol.com> wrote: > On Sat, 28 Feb 2015 20:42:35 -0600 Tony Harris wrote: > > > Hi all, > > > > I have a small cluster together and it's running fairly well (3 nodes, 21 > > osds). I'm looking to improve the write performance a bit though, which > > I was hoping that using SSDs for journals would do. But, I was wondering > > what people had as recommendations for SSDs to act as journal drives. > > If I read the docs on ceph.com correctly, I'll need 2 ssds per node > > (with 7 drives in each node, I think the recommendation was 1ssd per 4-5 > > drives?) so I'm looking for drives that will work well without breaking > > the bank for where I work (I'll probably have to purchase them myself > > and donate, so my budget is somewhat small). Any suggestions? I'd > > prefer one that can finish its write in a power outage case, the only > > one I know of off hand is the intel dcs3700 I think, but at $300 it's > > WAY above my affordability range. > > Firstly, an uneven number of OSDs (HDDs) per node will bite you in the > proverbial behind down the road when combined with journal SSDs, as one of > those SSDs will wear our faster than the other. > > Secondly, how many SSDs you need is basically a trade-off between price, > performance, endurance and limiting failure impact. > > I have cluster where I used 4 100GB DC S3700s with 8 HDD OSDs, optimizing > the write paths and IOPS and failure domain, but not the sequential speed > or cost. > > Depending on what your write load is and the expected lifetime of this > cluster, you might be able to get away with DC S3500s or even better the > new DC S3610s. > Keep in mind that buying a cheap, low endurance SSD now might cost you > more down the road if you have to replace it after a year (TBW/$). > > All the cheap alternatives to DC level SSDs tend to wear out too fast, > have no powercaps and tend to have unpredictable (caused by garbage > collection) and steadily decreasing performance. > > Christian > -- > Christian Balzer Network/Systems Engineer > ch...@gol.com Global OnLine Japan/Fusion Communications > http://www.gol.com/ >
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